1. FIELD OF INVENTION
The present invention relates to monitoring of torque in connections between tubular goods, particularly in the petroleum industry.
2. DESCRIPTION OF PRIOR ART
In the petroleum industry, failure of tubing or tubular goods has severe consequences. Replacing failed tubing in a well may often be more expensive than the expected value of oil or gas to be produced from the well. In gas wells where the gas is sour, containing hydrogen sulfide, a leak or failure in tubing could have fatal consequences.
Based on a study conducted some years past by a major oil company, it has long been customary in the connection, or make-up, of petroleum tubular goods with conventional, American Petroleum Institute, or API, specification threads to monitor both torque and turns of the tubular goods being made up. Unless both the torque and turns observed during make-up fell within specified limits of acceptability, a connection was rejected as unsatisfactory. Examples of this type of "torque-turns" monitoring are described in U.S. Pat. Nos. 3,368,396; 3,606,664; 3,745,820; 4,091,451; 4,176,436; 4,199,032; 4,208,775; 4,208,919 and 4,210,017. An article in Petroleum Engineering International, "Torque Turn in Principle and Practice", pp. 62 et al., July, 1980 provides a general summary of this technique.
As the petroleum industry has gone deeper into the earth in exploratory and production wells, higher pressures have been encountered. For this and other reasons, specially threaded connections known as premium connections have been used in petroleum industry tubular goods. This type of connection is based on metal-to-metal sealing or "shoulder" connect along specially shaped areas of the pin and box members being connected. As pressure increased in the tubular goods, metal-to-metal sealing contact increased in the premium connections. Examples of premium threaded connections are described in U.S. Pat. Nos. Re. 30,647 and 4,244,607.
However, torque-turn monitoring was not well adapted for premium connections, since shoulder could occur in a much smaller portion of a turn than the intervals, usually tenths, into which one revolution of a pipe was divided for monitoring turns. There have been indications that reducing the size of turn interval might help in shoulder contact detection, but this would require a substantial increase in the number of lugs or projections formed for turn interval division purposes on the rotary jaw member of the power tongs used in makeup of petroleum tubular goods.